1. Field of the Invention
The present invention relates to a curable organopolysiloxane composition. More specifically, this invention relates to a curable organopolysiloxane composition which has excellent adhesion.
2. Description of the Prior Art
A number of methods have been proposed for imparting adhesion to organopolysiloxane compositions which cure by an addition reaction between lower alkenyl radicals and silicon-bonded hydrogen atoms. The addition of either a silane containing a lower alkenyl radical and at least one silicon-bonded alkoxy group, or the addition of the partial hydrolyzate thereof is taught in U.S. Pat. No. 4,196,273, which issued to Imai et al on Apr. 1, 1980, Japanese Patent Publication No. 28,309/76, and U.S. Pat. No. 4,311,739, which issues to Hardman and Dujack on Jan. 19, 1982.
The addition of either a silane containing a silicon-bonded hydrogen atom and at least one silicon-bonded alkoxy group or a partial hydrolyzate thereof is taught in Japanese Patent Publication No. 5,836/82 which issued on Feb. 2, 1982.
The addition of a linear or cyclic polysiloxane which contains in each molecule a lower alkenyl radical or at least one silicon-bonded hydrogen atom in addition to at least one silicon-bonded alkoxy group and, optionally, groups such as the epoxy group or ester group, is taught in U.S. Pat. No. 3,699,072, which issued to Clark and Hayes on Jan. 11, 1972, U.S. Pat. No. 4,082,726, which issued to Mine and Okoyama on Apr. 4, 1978, Japanese Patent Publication No. 39,258/80; and Japanese Laid Open Patent Application (Koku) Nos. 58,756/79 and 58,755/79.
The addition of a mixture of an alkoxy-containing organosilicon compound, an organosilicon compound containing at least one silicon bonded hydrogen atom and an organotitanate is taught in U.S. Pat. No. 4,332,844, which issued to Hamada et al. on June 1, 1982.
U.S. Pat. No. 4,434,195, which issued to Skostins on Feb. 28, 1984 discloses using the combination of ethyl polysilicate and an acryloxysilane to improve the adhesion of peroxide-cured silicone rubber compositions to various substrates.
All of these prior art methods for achieving adequate adhesion to various substrates for organosiloxane compositions curable by a platinum-catalyzed hydrosilation reaction have not as yet been perfected, and problems remain in each case. In the case of the addition of silanes containing both lower alkenyl radicals and silicon-bonded alkoxy groups or partial hydrolyzates thereof, and in the case of the addition of siloxanes containing both lower alkenyl radicals and silicon-bonded alkoxy groups, the addition reaction is somewhat inhibited by the lower alkenyl groups, and the curing rate is slowed.
Siloxanes containing epoxy or ester groups are only slightly miscible with the main organopolysiloxane component, with the result that composition becomes opaque after such an addition. The trimethoxysilane disclosed in Japanese Patent Publication No. 5,836/82 is highly toxic. Furthermore, when this silane is added it generally evaporates from the organopolysiloxane composition during reduced pressure degassing.
The present inventor conducted investigations with a view to overcoming these problems in the prior art, and the present invention was developed as a result.
The objective of the present invention is to provide a curable organopolysiloxane composition which will tightly bond to various substrates without any of the disadvantages of compositions containing prior art adhesion promoters.